Roof jacks are provided to connect the outlet of a roof mounted air handler to an air duct which emerges from the roof. Prior art roof jacks are constructed to match the horizontally oriented opening in the bottom of the air handler to the slope of the roof. Generally, each roof jack must be specially constructed to fit the slope of the roof upon which it is to be used. However, roof jacks for flat roofs and for roof slopes of 4/12 (4 in 12; 4 units of vertical rise for each unit of horizontal run) are generally stocked by suppliers who deal in such devices because these are commonly used roof slopes. Even in those cases, the slope of the roof may be slightly deviant from the design value and a stock roof jack may not fit the angle perfectly. The misfit may cause air leakage from the system or may cause the roof mounted equipment to be mounted at a slight angle from the horizontal which could, in turn, cause problems in operation of the roof mounted equipment.
While suppliers could, and do different roof jacks to accommodate the full range of slopes which are encountered in the building industry, it is expensive to maintain such a large inventory, both in terms of the cost of the stock and the cost of storage space. The problem is even more critical when it is understood that there must be several different sizes (in terms of cross section) of roof jacks to meet the needs of various duct and exhaust outlet sizes which are encountered in roof mounted air handlers.
U.S. Pat. No. 3,742,659, by Drew, "Apparatus for Mounting Equipment on a Roof" (issued July 3, 1973), incorporates, as part of the invention therein described, an adjustable roof jack for a roof mounted air conditioner or the like. It comprises a first section which is attached to the roof and to the ducts emerging from the roof and a second section which connects to the bottom of the roof mounted equipment. The two sections are assembled in one of two orientarions with respect to each other and then the angle between the two sections is adjusted until the upper mounting surface is horizontal. The two sections are then fastened together to provide a solid platform for mounting the equipment and to provide an accurately angled duct between the equipment and the roof. While Drew's invention provides more than an adjustable roof jack, it must be noted that the roof jack portion of his invention, if adapted solely to that use, would use much more sheet metal in its construction than a fixed angle roof jack would use. This is true because Drew's design requires a large overlap in the sheet metal sections which serve as the upper and lower portions of the roof jack. A large part of the overlap is required to prevent water leakage between the sections and to provide a large range of angular adjustment.